Chemistry 312 Problem Set 6 (due Monday, August 15) key 1. a. Give the ground-state ligand-field electronic configuration for the populated valence molecular orbitals of the octahedral complex W(CO) 6 (no Jahn-Teller distortion). (a 1g ) 2 (e g ) 4 (t 1u ) 6 (t 2g ) 6 b. What is the term symbol (= term and multiplicity) for W in this state? Look on the Tanabe-Sugano diagram; the lowest term for d 6 is the ground state 5 D. c. Is the complex diamagnetic or paramagnetic? All electons are paired, so this complex is diamagnetic. d. The first electronic absorption band occurs at about 31,000 cm –1 . Assign this band to an electronic transition in the complex. The electronic transition is e g * ← t 2g . e. Calculate the wavelength (in nm) and the energy of this absorption (in kJ/mol). 31,000 cm –1 is a wavenumber, so the inverse of the wavenumber is the wavelength: (1/31,000 cm –1 )(10 9 nm/10 2 cm) = 323 nm. Then use E = hc/ λ = (6.626 × 10 –34 Js)(2.998 × 10 8 m/s)/(323 × 10 –9 m) = 6.15 × 10 –19 J = 370 kJ/mol. f. Is the photochemical dissociation of W(CO) 6 to W(CO) 5 + CO reasonable? Explain, in terms of the population of bonding and antibonding orbitals. The dissociation is reasonable because the photoexcitation of W(CO) 6 takes an electron from a bonding orbital (t 2g ) to an antibonding orbital (e g *) that is directed at the ligands. What this does is weaken the M-L bond.

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